Stanley Strother

Effects of irradiance, temperature and salinity on photosynthesis of Zostera muelleri

Physiological and biochemical knowledge of the Australian seagrass Zostera muelleri Irmisch ex Aschers. is scanty. Harvested samples of Z. muelleri have been used in physiological experiments to examine the effects of irradiance, temperature and salinity on apparent photosynthesis. Photosynthesis is significantly decreased by decreases in salinity and also by extremes of temperature. However, apparent photosynthesis is still maintained at a salinity 15% that of normal seawater and at temperatures of 3 and 30°C, consistent with the ecological role of Z. muelleri as an intertidal species.

The effect of pH on the inorganic carbon source for photosynthesis in the seagrass Zostera muelleri irmisch ex aschers

Abstract The ability of the seagrass Zostera muelleri Irmisch ex Aschers. to use HCO 3 − as well as CO 2 for photosynthesis was investigated by measuring photosynthetic O 2 evolution over a range of pH values. It was found that the apparent K m CO 2 fell from 0.128 mM at pH 7.9 to 0.016 mM at pH 9.1 indicating that HCO 3 − as well as CO 2 may act as a substrate for photosynthesis. The true K m CO 2 could not be determined due to inhibition of photosynthesis at pHs less than 7.8 K m CO 2 must be at least 0.128 mM, the apparent K m at pH 7.9, and is probably of the order of 0.200 mM CO 2 , the same as that reported for other marine plants. K m HCO 3 −1 is about 20 mM when CO 2 -dependent photosynthesis is minimal. Such a high K m HCO 3 − resembles values reported for freshwater, rather than marine plants. Photosynthetic O 2 evolution is not saturated with respect to total inorganic carbon in natural seawater (pH 8.2). It is suggested that the distinctive shoulder from pH 8.1 to 8.5 in the pH profile of photosynthetic O 2 evolution at a constant concentration of inorganic carbon is caused by an effect of pH on HCO 3 − uptake. The effect of pH on HCO 3 − uptake was determined by constructing a pH profile of photosynthesis at constant HCO 3 − concentration, and subtracting the estimated contribution of CO 2 to photosynthesis from this rate. The resultant curve has a maximum at pH 8.4 and declines sharply at pHs less than 8.

Seasonal changes in standing crop of Zostera muelleri in south-eastern Australia

Abstract The seagrass Zostera muelleri Irmisch ex Aschers. is a significant primary producer in shallow embayments and estuaries of south-eastern Australia. Seasonal influence on its growth is therefore of ecological importance. Estimates of above-ground (leaves, sheaths) and below-ground (roots, rhizomes) biomass were determined for Z. muelleri over a period of 18 months in order to study seasonal changes. A winter die-back was evident with the maximum difference between winter and summer above-ground biomass being sevenfold at Tip Island and 40-fold at Swan Bay Jetty. Although above-ground biomass was correlated with solar radiation, day length and maximum temperature, it was concluded that leaf growth rate is still a better correlate of seasonal change than biomass for Z. muelleri growing in south-eastern Australia.

Kinetic studies of lead(II) uptake by the seagrass Zostera muelleri in water by radiotracing, atomic absorption spectrometry and electrochemical techniques

Abstract Evidence was found that uptake of lead from seawater in both model and natural systems by the leaves of the seagrass Zostera muelleri does occur for live, dead and scraped leaves at all the lead concentrations tested. Positive uptake of lead was measured using the three analytical techniques of radio-tracer, differential pulse anodic stripping voltammetry and atomic absorption spectrometry; similar uptake profiles were obtained for each technique. Profiles always showed an initial rapid uptake phase followed by a gradual transition to a plateau phase at which an approximate equilibrium between lead attached to seagrass and free ionic lead in seawater was reached. The presence of active lead uptake processes was indicated in experiments which attempted to remove lead from leaves by a chelating agent.

The effects of temperature, salinity and seagrass species on the uptake of lead(II) from seawater by excised leaves

Abstract The dynamics of uptake by the leaves of seagrass species has been investigated by 210 Pb radiotracer techniques. The uptake of Pb from aqueous media per unit area of leaf by the seagrass Zostera muelleri was found to depend on temperature and salinity. Uptake was positively correlated with temperature. Pb uptake was greatest in distilled water and least in salinities exceeding normal seawater. The profile of uptake varied only slightly between three of the species studied, namely Zostera muelleri, Heterozostera tasmanica and Halophila australis , however, uptake by Lepilaena cylindrocarpa was considerably less than the other three species. The variations were examined in relation to microscopic anatomy especially in relation to the epidermis. The results are discussed in relation to possible mechanisms of the uptake of Pb by seagrass leaves. The results are consistent with the view that the seagrass leaves act as passive ion-exchange media during the course of Pb uptake.

Electrochemical reduction of the trimethyllead(IV) cation in seawater

Abstract The need to distinguish between inorganic and organic forms of lead in seawater has been widely recognized. Electrochemical techniques based on reduction at mercury electrodes or anodic stripping voltammetry have been proposed as methods for determining the various forms of lead. However, detailed investigation of the electrode process for the electrochemical reduction of the trimethyllead cation in seawater show that correct data may not necessarily be obtained with all electrochemical techniques. On the short time scale of polarography the proposed reduction mechanism is: (CH 3 ) 3 Pb + + e (CH 3 ) 3 Pb+3 Hg→Pb(amalgam)+3 CH 3 Hg(ads) 3 CH 3 Hg(ads)+3 e →3 CH 3 Hg − Data show that differential pulse polarography can be used to determine simultaneously inorganic lead and the trimethyllead cation, however, with inverse oxidation experiments involving stripping of lead (amalgam) such as reverse normal pulse voltammetry, substantial modification to the electrode process occurs in the presence of methylated mercury. Anodic stripping voltammetry therefore suffers from substantial interference, when using the: Pb(amalgam)Pb 2+ +2 e electrode process for determining the concentration of the trimethyllead cation in seawater.

Seasonal changes in leaf growth rate of Zostera muelleri Irmisch ex Aschers. In South-Eastern Australia

The seagrass Zostera muelleri Irmisch ex Aschers. is an important primary producer in shallow embayments of south-eastern mainland Australia and Tasmania. Seasonal influence on its growth is therefore of ecological importance. In situ leaf growth rates have been determined for Zostera muelleri over a period of 18 months in order to study seasonal changes. In winter, growth rates of 2–3 mm day−1 shoot−1 were observed compared with 7–8 mm day−1 shoot−1 in summer. The plastochrone interval varied from as low as about 7 days in summer to about 29 days in winter. Leaf growth was correlated more highly with mean solar radiation and daylenght than with temperature. Some variation occurred between sites, possibly owing to differences in exposure to winds and length of time of seagrass emergence during the tidal cycle.

Xylem exudate concentrations of cofactor nutrients in grapevine are correlated with exudation rate

Abstract Xylem exudates collected from the cut canes of Vitis vin‐ifera L. var. Waltham Cross for 10 weeks around the time of budburst were analyzed for nutrient concentrations. The seasonal variations of the inorganic constituents examined [phosphorus (P), calcium (Ca), potassium (K), magnesium (Mg), manganese (Mn), zinc (Zn), iron (Fe), copper (Cu), sodium (Na), and chlorine (Cl)] are presented and discussed with respect to the metabolic needs of the plant as it breaks dormancy. Of particular interest was the observation that some of the nutrients (Ca, K, Mg, Mn, Zn, and Fe) showed similar seasonal variations in their concentrations. These variations were significantly correlated with the rate of xylem exudate flow. Other essential nutrients which are not enzyme cofactors did not show this variation. We propose that these variations, similar to the previously noted variation of organic acids in grapevine xylem exudate, reflect a flow‐dependent uptake and/or remobilization of nutrients to facilitate budb...

Phosphatases from pollen of Brassica campestris and Lilium regale

Abstract Soluble and wall-bound acid phosphatases isolated from rape seed pollen showed similar properties except for the pH optimum curve which was elevated for the cell wall enzyme. About 50 % of the phosphatase activity of washed pollen wall preparations could be solubilized with Triton X-100, compared with only ca 20% for the corresponding preparation from lily pollen. A comparison of the wall-bound acid phosphatase of rape seed and lily pollen showed a marked difference in specificity towards fructose-6-phosphate and glucose-6-phosphate. A Mg 2+ -dependent alkaline pyrophosphatase was obtained from rape seed pollen but this activity could not be detected in cell wall preparations.

Growth inhibition of Lemna minor L. by hydrolysates of gum karaya

Abstract Hydrolysates of gum karaya, a commercially available polysaccharide, were shown to inhibit ( P Lemna minor L. in axenic culture. The hydrolysates were dialysed using 1000 Da cutoff tubing to remove low molecular weight material such as monosaccharides and small oligosaccharides. Controls using glucose subjected to the same hydrolysis procedure did not show any inhibition compared with untreated control flasks. The growth inhibition was associated with severe chlorosis of the Lemna fronds raising the possibility that this fraction could be developed as a biodegradable herbicide for aquatic plants. Gel permeation chromatography indicated that an anthrone-positive peak was eluted from the column in a position consistent with its being an oligosaccharide or a mixture of oligosaccharides. Samples of the peak eluate were inhibitory to the growth of L. minor and caused bleaching of fronds.